Friday, September 30, 2011

Tennessee BBS 6: Gnatcatchers to Waxwings

Still another common species that has shown a large increase in numbers on Tennessee BBS routes. Gnatcatcher counts have increased steadily by roughly a factor of four.

Eastern Bluebird

35 year change: +9.73 (+146%) ± 1.54

Though the first decade or so of the BBS appeared to show a decline in Bluebirds in Tennessee, in 1979 this turned and the overall trend for the BBS era has been strongly upwards.

Veery

35 year change: +0.01 ± 0.01

Recorded only on the Fish Springs route and only in a few years, the Veery data provide little information.

Wood Thrush

35 year change: -2.25 (-24%) ± 1.02

Wood Thrushes have declined modestly since the inception of the BBS, with most of this drop taking place between 1975 and 1990. Numbers have been quite stable in recent decades.

American Robin

35 year change: +13.21 (+113%) ± 4.36

Robin numbers increased steadily until about 1990 and have remained approximately stable since then. This is now one of the most widespread and abundant species on Tennessee BBS routes.

Gray Catbird

35 year change: -3.04 (-71%) ± 0.42

Catbirds have declined throughout the BBS period, with an especially steep drop during the 1980s. Present day counts are barely a quarter of what they were in the 1960s.

Northern Mockingbird

35 year change: -4.32 (-16%) ± 1.59

There has been a small but statistically significant drop in Mockingbird numbers, most of which took place before 1980. Mockingbirds remain abundant and widespread with stable counts in recent decades.

Brown Thrasher

35 year change: -1.15 (-21%) ± 0.68

Thrashers have also shown a small but statistically significant decline through the period.

European Starling

35 year change: +8.14 (+15%) ± 9.78

Though Starling numbers appear to have fluctuated somewhat, the change across the entire BBS era is not statistically significant. They were abundant in the 1960s, and remained just as abundant in the 2000s.

Cedar Waxwing

35 year change: +2.28 (+871%) ± 1.12

Waxwing numbers underwent a rapid shift during the late 1980s and early 1990s from a low, stable level to a much higher and more variable plateau.